Polymer finisher

ABSTRACT

Apparatus for finishing viscous materials, as in polycondensation reactions for the production of polyamides and polyesters wherein a low viscosity liquid is fed into one end of a cylindrical vessel having one or more vapor outlets and at least one horizontally mounted agitator, mounted for rotation within said vessel, and having a drive shaft running throughout the full length of said vessel having spoked wheels interspaced and interconnected by circularly arranged serrated blades, said wheels being spaced closer together at the feed end and being spaced at greater distances towards a discharge port located at the opposite end from the feed end of said vessel, said serrated blades being located in such a way as to keep a close clearance between the blade and wall and thus maintain a continuous shear gradient between blade and wall, and carry an amount of liquid with them each time they leave the liquid surface which is poured from the blade near the apex of its travel and in this manner an unsupported corrugated film is formed parallel to the axis of the drive shaft yielding a large surface area which aids in rapid evaporation of volatile material thus expediting the polycondensation reaction.

United States Patent Saunders et al.

[ Aug. 29, 1972 [54] POLYMER FINISHER [72] Inventors: Leonard Vktor JohnSaunders,

Richmond, Va.; David Rochell, Sarnia, Ontario, Canada [73] Assignee:Allied Chemical Corporation, New

York, NY.

[22] Filed: Nov. 19, 1970 [21] Appl. No.: 90,977

Primary Examiner-John Adee Attorney-Luther A. Marsh and Roy H.Massengill [57] ABSTRACT Apparatus for finishing viscous materials, asin polycondensation reactions for the production of polyamides andpolyesters wherein a low viscosity liquid is fed into one end of acylindrical vessel having one or more vapor outlets and at least onehorizontally mounted agitator, mounted for rotation within said vessel,and having a drive shaft running throughout the full length of saidvessel having spoked wheels interspaced and interconnected by circularlyarranged serrated blades, said wheels being spaced closer together atthe feed end and being spaced at greater distances towards a dischargeport located at the opposite end from the feed end of said vessel, saidserrated blades being located in such a way as to keep a close clearancebetween the blade and wall and thus maintain a continuous shear gradientbetween blade and wall, and carry an amount of liquid with them eachtime they leave the liquid surface which is poured from the blade nearthe apex of its travel and in this manner an unsupported corrugated filmis formed parallel to the axis of the drive shaft yielding a largesurface area which aids in rapid evaporation of volatile material thusexpediting the polycondensation reaction.

7 Claims, 5 Drawing Figures mtmc'muszs I912 3.686326 Z l6 g i 4 4 1 FIG.4 FIG 5 INVENTOR.

L.V.J. SAUNDERS DAVID ROCHELL irrio" I ATTIORNEY POLYMER FINISHERBACKGROUND OF THE INVENTION This invention relates to a method and anapparatus for the conversion of liquid of low viscosity into a liquid ofhigh viscosity. More particularly, this invention relates to a methodand an apparatus for the conversion of liquid of low viscosity into aliquid of high viscosity by removing volatile material during saidconversion while maintaining a continuous shear gradient between rotorand wall and preventing build-up of degradation products. Even moreparticularly, this invention relates to a method and an apparatus toconvert low viscosity liquid into a very high viscosity range to producepolymer of fiber-grade viscosity. Still more particularly, it relates todegassing or removal of volatiles from a mixture being polymerized bycondensation in which serrated substantially radial scoop blades aremoved through the liquid while remaining parallel to the level of theliquid and that become traverse to the level of the liquid upon leavingthe liquid, thus forming an unsupported film for degassing and theremoval of volatiles.

The degassing and removing of volatiles from condensation type reactionsare known. As more stringent requirements are continuously being placedupon quality of polymeric materials, greater and more thorough studiesare being made in an effort to produce the quality necessary andrequired. One such effort is shown in U.S. Pat. No. 3,358,422, whichissued on Dec. 19, I967. The patentee here illustrates the degassing ofa viscous liquid polymer reaction mass during the intermediatepolycondensation stages. In this patented process the rod-like memberswere utilized specifically for the purpose of filming a viscous liquidwithin a very specific viscosity range, namely, between and 500 poises.If the viscosity is less than 30 poises or more than 500 poises nocontinuous film can be drawn from the liquid mass and thus the apparatusis inoperable. Other similar, yet quite specific efforts have beenundertaken as depicted in US. Pat. Nos. 2,758,915 and 2,869,838, andothers. To prepare a polymer having substantially all volatiles removedwhile maintaining a continuous reaction gradient with substantially nodegradation while producing a polycondensation polymer up to 30,000poises would make a substantial contribution to this highly complex art.

It is therefore a prime object of this invention to provide an improvedpolymer finisher apparatus and method for producing an improved fibergrade polymer.

A further object of this invention is to provide an improved polymerfinisher apparatus and method for producing an improved fiber gradepolymer wherein substantially all volatile material is removed, acontinuous shear gradient is maintained while substantially nodegradation of said polymer occurs.

Other objects and a more complete understanding of the present inventioncan be had by referring to the following description and claims.

SUMMARY OF THE INVENTION According to the present invention there isprovided a cylindrical vessel for finishing liquid viscous materialwhich is provided with an inlet and outlet for said material at oppositeends of said vessel, and at least one outlet for the removal of volatilematerial, a rotatable shaft mounted substantially concentric with thecylindrical axis for rotation within said vessel and having a driveshaft for rotating said shaft, said shaft having spoked wheelsinterspaced and interconnected by circularly arranged serratedsubstantially radial scoop blades, said wheels being interspaced closernearer the feed end and being gradually spaced at greater distancesnearer the outlet end of said vessel, said blades being so positioned asto maintain a close clearance from the inside surface of said vessel,maintain a continuous shear gradient, and carry an amount of saidmaterial with them each time they leave the liquid surface forming anunsupported corrugated film parallel to the axis of said drive shaftthen yielding a large surface area for rapid evaporation of volatilematerial thus expediting the finishing of said liquid viscous material.

A better understanding of the nature and objects of this invention willbe seen when reference is made to the following detailed descriptiontaken in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal axial section of a cylindrical polymerizationvessel with cylindrical agitator shown in elevation;

FIG. 2 is a perspective view of one example of the spoked wheel ordynamic bafile showing the spokes of the wheel, the drive shaft, theserrated blades attached to said wheel and the blade alignment angle 15necessary for forming an unsupported film parallel to theaxis of saiddrive shaft;

FIG. 3 is a perspective view of the serrated edge of the blade usefulfor an embodiment of the present invention and wherein it is attached;

FIG. 4 is an enlarged perspective view of the variations of theserrations of the blade edge useful for an embodiment of the presentinvention; and

FIG. 5 is an enlarged view of one blade or scoop useful for anembodiment of the present invention.

FIG. 1 shows in longitudinal. sectional elevation agitation apparatususeful according to the present invention. Vessel 2 has inlet 4 andoutlet 6 which may be located other than as shown, but must be onopposite ends of vessel 2. Such inlet 4 and outlet 6 located nearopposite ends of the vessel are to receive and discharge the processliquid. A vent 8 located at the top of vessel 2 may have more than onevessel exit as required for process purposes. The agitator 10 located ina rotatable manner in vessel 2 is mounted through journals, not shown,by shaft 12 and contains spoked wheel or dynamic baffle 14 havingserrated blades 16. The blades 16, more specifically shown in FIG. 2 areso positioned on wheel or dynamic bafile 14 in such a way as to have analignment angle 15 from about 10 to about 30. The number of blades 16 ineach compartment of vessel 2 can vary from about six to about 16 and canvary in number from the inlet section 18 to the outlet end section 20 ofvessel 2. Each blade has a serration 22 more specifically shown in FIG.3 and FIG. 4 on its outer edge and the serrations also can vary inwidth, depth and number from the inlet to the outlet end of vessel 2.FIG. 5 illustrates a single enlarged view of one blade 16 illustratingradial curvature. Each blade 16 is firmly attached to each dynamicbaffle 14 at the proper alignment angle 15 in order to keep a closeclearance between the blade 16 and the interior wall 24.

Operation bf this apparatus, which is especially adapted to function asa reactor finisher for condensation polymerization, can readily beunderstood. Liquid feed polymer of comparatively low viscosity is forcedby suitable means into the inlet end 4 of vessel 2 and passes to theother end and out vessel outlet 6, the flow being effected by theinterrelationship of the various components of the apparatus with thepolymeric liquid material being finished. No pumping, as such is broughtabout by the various components of the apparatus and their relationshipwith one another and the liquid being processed of the invention, but anormal flow is obtained commensurate with the amount of material fed tothe reactor finisher. The forward movement is the result only of theaddition of fresh material to the feed end of the reactor. This thenretains the plug flow parameter which is desirable to give equalexposure to the environment forevery element of the polymer melt. Theeffect of the compartments of the rotor is to give extensive peripheralmixing while minimizing axial mixing, again reinforcing the plug flowprinciple which is approximated practically by a large number ofperfectly mixed stages, mounted in series. No forward movement orpumping action is brought about by the rotation of the rotor or agitatoritself.

The unsupported corrugated film of this invention yields an improveddegassed polymeric material because the film tends to be turbulentwithin itself which contributes to a good mass transfer rate between thefilm and the vapor, the film is available for mass transfer over allexposed surfaces and significantly greater than heretofore, the film inthis way is made very thin which minimizes resistance to mass transfer,there is no supporting surface for flow stagnation and degradationproducts to build up the corrugation given to the film yields muchlarger surface area than heretofore with all its attendant advantages.

The corrugation given to the unsupported film is brought about by theserrations and the designated alignment angle 15. They yield aconsistent corrugated film across the blade which is formed by polymerflowing over the serrations of the blade and forming a corrugatedappearing film. The blade is preferably horizontal to prevent morematerial spilling over one end in an axial sense and giving an uneven orthick and thin type filming. The serrated blade of this inventioneliminates blockage and thus is self-cleaning by angle adjustment anddegree of curvature by the melt pool through which it passes upon eachrevolution. Thus the serrated blades of this invention yield effectivemeans for degassing higher viscosity materials. The angle and curvatureis optimized so that sufficient material is cartied to form a filmcontinuously right across the reactor finisher periphery, and yet justbe exhausted by the time it reenters the melt pool to pick up a freshload. The blade dumps the exposed material on top of the melt pool butpicks up fresh material to be degassed from the bottom of the melt pool,thus accentuating'the intra-stage mixing.

The feed polymer utilized in the operation of this invention may be aslow as 100 poises in viscosity. The finished product viscosity may rangeup to 30,000 poises after the polycondensation reaction is substantiallycomplete. The agitator 10 speed can vary from between 0.1 rpm to about15 rpm depending upon the polymer viscosity. The clearance between theblade 16 and the vessel interior wall 24 can be as low as one-sixteenthinch in order to allow continual wiping of the surface thus eliminatingany polymer buildup and thus preventing any polymer degradation from anysuch polymer buildup as it would be subject to excessive exposure tohigh temperature and vacuum with subsequent polymerization and thermaldegradation. The apparatus is more preferably operated at vacuum levelsbetween 0.1 mm Hg absolute and 50 mm Hg; however, it may be operatedusing an atmosphere of nitrogen or steam and under pressure if necessaryfor process reasons. The normal operating liquid level of vessel 2 canbe between about 10 and about 60 percent of said vessel.

The blade 16 design of the apparatus of this invention is of criticalsignificance. The design of the blade 16 along with the spoked typewheel or baffle 14 wherein it is attached allows for a rigid typeconstruction thus yielding a stiffer shaft 12 so no essential variancecan occur thus upsetting process conditions. The blades 16 arepositioned in peripheral slots of the baffies or wheels 14 and preparedwith serrations 22 of sufficient width and depth to provide gooddistribution along the entire length of blade 16 during the entireperipheral travel of the rotor blades. Preferably, a one foot space isprovided at the inlet end and a two foot space is provided at the exitend of the vessel wherein a pool is allowed to form for subsequent feedpurposes from said vessel. This allows plug flow to be maintained at alltimes during operation. The exit end of the vessel is provided with atwo or twin flight screw or a four arm spider which is attached to theshaft with plows on the outer ends to allow continual wiping of the endwall thus eliminating any polymer buildup at this point.

The blade design angle with reference to obtaining best performance isalso critical. In order to obtain proper filming the blade angle issubstantially radial, not circumferential, thus allowing filmingcontinuously from the time it leaves the polymer melt until it againenters the polymer melt. Further, it allows continuous filming withoutany film supporting means. The blade alignment angle 15 or scoopcurvature adjustment can vary from about 11 to about 30. The alignmentangle 15 is defined as that angle tangent to the scoop and the radius ofthe wheel.

Another feature of this invention relates to the open area or distancebetween the spoked wheels or dynamic baffles. The distance can vary fromabout 2 inches to about 36 inches and provides further surfacegeneration and also acts as a barrier to co-axial mixing betweencompartments. Further, this area is of such a diameter to preventpulsing of polymer backward and forward between compartments or bypassing, and, at the same time enables a definite flow forwardequivalent to the initial polymer feed rate. Such design, allowing aminimum of backmixing between adjacent compartments is required tomaximize the approach to plug flow and product quality. Further, thewheels or dynamic baffles are supported from the shaft by spokes whichallow forward movement of the liquid while giving necessary support tothe wheels and blades.

The apparatus of the invention is particularly suited for the productionof polyamides and polyesters; however, it is equally suitable for anypolycondensation material that volatiles evolved during polycondensationmust be efiiciently removed.

We claim:

1. Apparatus for finishing liquid viscous material radial scoop blades,said blades having a specified curvature alignment angle, said wheelsbeing interspaced closer nearer the feed end and being spaced at greaterdistances nearer the outlet end of said vessel, said blades being sopositioned as to keep a close clearance between the blade and the insidewall of said vessel, maintain a continuous shear gradient between theblade and inside vessel wall, and carry an amount of said liquidmaterial with them each time they leave the liquid surface forming anunsupported corrugated film parallel to the axis of said drive shaftthus yielding a large surface area for rapid evaporation of volatilematerial thus expediting the finishing of said liquid viscous material.

2. The apparatus as defined in claim 1 wherein the scoop curvaturealignment angle is from about to about 30.

3. The apparatus as defined in claim 1 wherein the serration size inboth width and depth can be adjusted for control of film thickness ofthe viscous material.

4. The apparatus as defined in claim 1 wherein the agitator componentsare so interrelated and positioned in relation to said material that nopumping of the viscous material takes place.

5. The apparatus as defined in claim 1 wherein agitator components areso interrelated to said vessel to continually remove material beingprocessed from the interior surfaces of the vessel as the agitatorrotates.

6. The apparatus as defined in claim 1 wherein the scoop curvaturealignment can vary from the feed end of the vessel to discharge end ofthe: vessel.

7. A process for the continuous polycondensation of a liquid viscousmaterial having a viscosity in the range of up to 30,000 poisesconsisting of a linear saturated or unsaturated polyester or polyamideby heating the melt under pressure and wherein it is desired to effectdegassing of said materials with consequent removal of volatilematerials, comprising the steps of:

a a. continuously feeding a quantity of the liquid into an inlet chamberof a revolving cylindrical agitator within a vessel;

. controlling and maintaining liquid quantity input with liquid quantityoutput said chamber to a liquid level within said vessel of from about10 to about 60 percent thereof;

. lifting continuously a quantity of the liquid as an unsupportedcorrugated film in a continuous movement substantially perpendicular tothe surface of said liquid by passing an elongate member through saidmaterial havin spoked wheels interspace and interconnected y circularlyarranged serrated substantially radial scoop blades having a designatedalignment angle in relation to the wheel wherein it is attached;

d. stretching said unsupported film within each chamber of said vesselcontinuously from the exit point of said liquid until reentry of saidunsupported film on the side opposite the exit point of said liquid byplacement and interrelationship of each compartment component inrelation to the liquid material being processed and the speed in whichthe agitator is revolved; evacuating continuously volatile materialsduring said polycondensation, and f. recovering said degassed liquidviscous material.

2. The apparatus as defined in claim 1 wherein the scoop curvaturealignment angle is from about 10* to about 30*.
 3. The apparatus asdefined in claim 1 wherein the serration size in both width and depthcan be adjusted for control of film thickness of the viscous material.4. The apparatus as defined in claim 1 wherein the agitator componentsare so interrelated and positioned in relation to said material that nopumping of the viscous material takes place.
 5. The apparatus as definedin claim 1 wherein agitator components are so interrelated to saidvessel to continually remove material being processed from the interiorsurfaces of the vessel as the agitator rotates.
 6. The apparatus asdefined in claim 1 wherein the scoop curvature alignment can vary fromthe feed end of the vessel to discharge end of the vessel.
 7. A processfor the continuous polycondensation of a liquid viscous material havinga viscosity in the range of up to 30,000 poises consisting of a linearsaturated or unsaturated polyester or polyamide by heating the meltunder pressure and wherein it is desired to effect degassing of saidmaterials with consequent removal of volatile materials, comprising thesteps of: a. continuously feeding a quantity of the liquid into an inletchamber of a revolving cylindrical agitator within a vessel; b.controlling and maintaining liquid quantity input with liquid quantityoutput within said chamber to a liquid level within said vessel of fromabout 10 to about 60 percent thereof; c. lifting continuously a quantityof the liquid as an unsupported corrugated film in a continuous movementsubstantially perpendicular to the surface of said liquid by passing anelongate member through said material having spoked wheels interspacedand interconnected by circularly arranged serrated substantially radialscoop blades having a designated alignment angle in relation to thewheel wherein it is attached; d. stretching said unsupported film withineach chamber of said vessel continuously from the exit point of saidliquid until reentry of said unsupported film on the side opposite theexit point of said liquid by placement and interrelationship of eachcompartment component in relation to the liquid material being processedand the speed in which the agitator is revolved; e. evacuatingcontinuously volatile materials during said polycondensation, and f.recovering said degassed liquid viscous material.